1. Field of the Invention
The present invention relates to a nonwoven fabric of longitudinally aligned filaments, a nonwoven fabric produced by longitudinally stretching such a nonwoven fabric of longitudinally aligned filaments, and a method of and an apparatus for manufacturing such nonwoven fabrics.
Nonwoven fabrics according to the present invention are excellent in mechanical strength and dimensional stability, and can be used as a material web for nonwoven fabrics that are strong in one direction and perpendicularly crossed nonwoven fabrics.
2. Description of the Related Art
Known processes for manufacturing nonwoven fabrics include a spunbond process, a melt-blow process, and a spunlace process for processing spun yarns directly into nonwoven fabrics. Nonwoven fabrics manufactured by these processes are referred to as spunbonded nonwoven fabrics in a wide sense. The nonwoven fabrics manufactured by these processes are the mainstream of nonwoven fabrics as they are economical and mass-producible.
The spunbonded nonwoven fabrics in a wide sense are randomly nonwoven fabrics in which filaments are randomly aligned. Many of those spunbonded nonwoven fabrics are of small mechanical strength and have no dimensional stability. The inventors of the present invention have devised a process of stretching a nonwoven fabric and a process of manufacturing a nonwoven fabric which comprise laminated perpendicularly crossed nonwoven fabrics in order to eliminate the drawbacks of conventional nonwoven fabrics (see Japanese patent publication No. 36948/92 and Japanese laid-open patent publication No. 204767/98 for details).
Japanese patent publication No. 25541/84 discloses a process of aligning filaments in one direction by inclining a conveyor to the direction in which the filaments are ejected. Japanese laid-open patent publication No. 3604/95 reveals a process of depositing filaments ejected with an air stream on an air-permeable conveyor and controlling the air stream with an air stream blocking device disposed behind the conveyor for thereby spreading the filaments in the longitudinal direction to improve alignability of the filaments.
However, the above conventional processes fail to sufficiently align filaments to a high degree. Particularly, according to the process disclosed in Japanese laid-open patent publication No. 3604/95, since the air flows along the gradient of the conveyor and the ejected air is not drawn and removed at a most important spot where the filaments are placed on the conveyor, the filaments tend to flow on the conveyor due to the ejected air that has reached the conveyor, and the filaments are liable to be disarranged. Stated otherwise, it is necessary to prevent the filaments from being disarranged on the conveyor in order to manufacture a longitudinally aligned nonwoven fabric of highly aligned filaments.
Generally, in order to produce a nonwoven fabric of filaments that are sufficiently aligned longitudinally, it is not sufficient to align the filaments longitudinally in the spinning process. The best way of improving the alignment of filaments is to stretch the nonwoven fabric in the longitudinal direction. However, after the spinning process, the nonwoven fabric cannot well be stretched longitudinally because the filaments are not well aligned longitudinally and are not sufficiently cooled, and it is difficult to stretch the nonwoven fabric to high mechanical strength at a high magnification.
It is an object of the present invention to provide a method of and an apparatus for manufacturing a longitudinally aligned nonwoven fabric that filaments are highly aligned longitudinally.
Another object of the present invention is to provide a method of and an apparatus for manufacturing a longitudinally stretched nonwoven fabric by further stretching a longitudinally aligned nonwoven fabric longitudinally for increased mechanical strength.
To achieve the above objects, a method of manufacturing a longitudinally aligned nonwoven fabric according to the present invention comprises the steps of preparing a group of nozzles for extruding a plurality of filaments, and a conveyor for collecting and delivering the filaments extruded from the group of nozzles, carrying the filaments extruded from the group of nozzles with a high-speed air stream to attenuate the filaments, and periodically changing the direction of the high-speed air stream in the machine direction of the conveyor.
An apparatus for manufacturing a longitudinally aligned nonwoven fabric according to the present invention comprises a spinning mechanism for extruding a plurality of filaments from nozzles, a high-speed air stream generating mechanism for generating a high-speed air stream to carry the filaments extruded from the nozzles to attenuate the filaments, a conveyor for collecting and delivering the filaments attenuated by the high-speed air stream, and at least one air stream vibrating mechanism for periodically changing the direction of the high-speed air stream in the machine direction of the conveyor.
The filaments extruded from the nozzles are attenuated by the high-speed air stream and collected on the conveyor. Since the direction of the high-speed air stream is periodically changed in the machine direction of the conveyor, i.e., in the longitudinal direction, the filaments carried by the high-speed air stream are periodically vibrated in the longitudinal direction, and partially folded over themselves in the longitudinal direction as they are collected on the conveyor. As a consequence, a nonwoven fabric in which filaments are well aligned is produced.
According to the present invention, for spinning the nonwoven fabric, a spunbond process in a wide sense is employed because the spunbond process is the most refined spinning process and excellent both economically and for its mass-producibility. The spunbond process in the wide sense resides in that molten filaments, i.e., filaments molten with heat, rather than being dissolved in a solvent, are drafted at a high magnification and attenuated by a high-speed air stream whose speed is close to the sonic speed.
As a result of studies made by the inventors, it has been found that the alignment of the filaments can be improved by periodically changing the direction of the high-speed air stream used to attenuate the filaments in the machine direction of the conveyor, and that the direction of the high-speed air stream can easily be changed based on the Coanda effect. According to a preferred embodiment, an air stream vibrating mechanism is disposed in a region where the high-speed air stream flows, the air stream vibrating mechanism having a wall surface, at least one of the direction of the wall surface with respect to the direction of the high-speed air stream and the distance of the wall surface from the direction of the high-speed air stream being variable, or alternatively, an air stream vibrating mechanism is disposed which has a wall surface inclined to the direction of the high-speed air stream, the distance between the wall surface and the air stream axis of the high-speed air stream being variable.
By cooling, with a mist, the high-speed air stream which has been supplied at a temperature equal to or higher than the melting point of the material of the filaments, the filaments carried and attenuated by the high-speed air stream can be cooled before their molecules are aligned in the longitudinal direction. As a result, when the nonwoven fabric is subsequently stretched in the longitudinal direction, the nonwoven fabric can be stretched to an increased extent.
According to the present invention, there are also provided a method of and an apparatus for manufacturing a longitudinally stretched nonwoven fabric.
The method of manufacturing a longitudinally stretched nonwoven fabric comprises the steps of manufacturing a longitudinally aligned nonwoven fabric by the above method of manufacturing a longitudinally aligned nonwoven fabric, and longitudinally stretching the longitudinally aligned nonwoven fabric.
The apparatus for manufacturing a longitudinally stretched nonwoven fabric comprises the above apparatus for manufacturing a longitudinally aligned nonwoven fabric, and a device for longitudinally stretching the longitudinally aligned nonwoven fabric manufactured by the apparatus for manufacturing a longitudinally aligned nonwoven fabric.
With the method of and the apparatus for manufacturing a longitudinally stretched nonwoven fabric, since the nonwoven fabric of filaments that have been highly aligned in the longitudinal direction is further stretched in the longitudinal direction, a nonwoven fabric that is excellent in mechanical strength in the longitudinal direction can be produced.
In the explanation of the direction in which the filaments are aligned and stretched, the term xe2x80x9clongitudinal directionxe2x80x9d means the machine direction in which the nonwoven fabric is manufactured, i.e., the direction in which the nonwoven fabric is fed, and the term xe2x80x9ctransverse directionxe2x80x9d means the direction perpendicular to the longitudinal direction, i.e., the direction transversely across the nonwoven fabric.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings, which illustrate examples of the present invention.